It is known that, by color development of a silver halide color photographic material, the oxidation product of an aromtic primary amine developing agent reacts with a coupler to form a dye such as an indophenol, an indoaniline, an indamine, an azomethine, a phenoxazine, a quinonimine, a phenazine, and the like, thus forming a color image (for example, see T. H. James, The Theory of the Photographic Process, 3rd Edition, pages 382 to 396, Macmillan Co., New York (1971)). In this procedure, the subtractive color process is ordinarily used for color reproduction, and silver halide emulsions which are selectively sensitive to blue, green and red light, and yellow, magenta and cyan color image formers, which are respectively the complementary colors of blue, green and red, are employed. For example, a coupler of the acylacetanilide, malondianilide or dibenzoylmethane type is used for forming a yellow color image; coupler of the pyrazolone, pyrazolobenzimidazole, cyanoacetophenone, pyrazolotriazole or indazolone type is generally used for forming a magenta color image; and a phenolic coupler, such as a phenol and a naphthol, is used for forming a cyan color image.
Usually, color photographic light-sensitive materials are roughly divided into two classes, one of which is a coupler-in-developer type color photographic light-sensitive material wherein a coupler is present in the developing solution and the other of which is an incorporated coupler type color photographic light-sensitive material wherein a coupler is incorporated into each light-sensitive layer of the photographic maerial so as to maintain the independent functions thereof. In the latter type of photographic material, a dye image forming coupler is added to a silver halide emulsion layer. The coupler added to an emulsion layer must be rendered non-diffusible (diffusion-resistant) in the binder matrix of the emulsion layer.
On the other hand, a two-equivalent coupler in which a group capable of being released as a result of the coupling reaction with an oxidation product of a developing agent is substituted at the coupling position thereof has been also known. A two-equivalent coupler can form one mole of dye using two moles of silver although at least four moles of silver are required by a four-equivalent coupler in order to form one mole of dye. Therefore, it is possible to reduce the amount of silver coated in the photographic light-sensitive material resulting in a decrease in production cost and a reduction in the film thickness by employing a two-equivalent coupler.
Although known two-equivalent couplers have good characteristics to some extent, improvement in their properties is still desired. In particular, known two-equivalent couplers have insufficient color forming properties which are important in high temperature rapid processing that has recently become populer. In order to compensate for the insufficient color forming properties, an organic solvent such as benzyl alcohol, etc. has been added to a developing solution, if desired. However, organic solvents used to accelerate color formation have several problems. For example, (1) since they are absorbed into emulsion layers during development the amount thereof decreases in the developing solution and thus the color formation becomes poor, (2) they are carried over into a bleaching solution of a bleach-fixing solution and hinder removal of silver or a decrease in dye density results (3) they remain in the photographic material after processing and adversely affect the fastness of dye images, and (4) they are mixed in processing wastes and cause an increase in BOD and COD of the wastes.
For these reasons it has been eagerly desired to eliminate the use organic solvents to accelerate color formation or reduce the amount thereof.
Recently, couplers containing a diffusion-resistant group having a p-hydroxyphenylsulfonyl group or a p-hydroxyphenylsulfinyl group as a terminal group as described in Japanese Patent Application (OPI) No. 42045/83 have been proposed. These couplers are recognized to have improved color forming properties in comparison with conventionally known couplers due to the functions of the diffusion-resistant group. However, the improvement achieved is still not sufficient and they are disadvantageous because they have a low solubility in the organic solvents used for dispersing couplers.